1. Field of the Invention
The present invention relates to electronic sphygmomanometers, and particularly to an electronic sphygmomanometer capable of adjusting the pressure release rate of a cuff during measurement.
2. Description of the Background Art
One of sphygmomanometers which have long been well-known is a mercury type sphygmomanometer. By such a mercury sphygmomanometer, pressure is applied to a cuff so as to pressurize a blood vessel. In a following decompression process in which air is discharged from the cuff to release the pressure therefrom, drop of mercury is watched, the systolic pressure or maximum blood pressure is determined by detection of K (Korotkoff) sounds with a stethoscope by a person who measures (e.g. physician) and the diastolic pressure or the minimum blood pressure is determined by ceasing of the K-sounds. There is also an electronic sphygmomanometer which electronically measures blood pressure by detecting K-sounds with a sensor.
In the decompression process of these sphygmomanometers, the air is discharged relatively slowly, in other words, the air discharge rate is slow, in order to ensure and facilitate detection of K-sounds. However, the slow air discharge rate prolongs the period from detection to ceasing of K-sounds and accordingly measurement takes too much time, which would cause pain to a subject person. Therefore, when a skilled operator who measures takes blood pressure measurement by using the mercury sphygmomanometer, the operator decreases the cuff pressure first at a constant pressure release rate to determine the systolic pressure by the first occurring K-sounds, then opens an air vent valve to temporarily increase the pressure release rate and accordingly decrease the pressure immediately to a pressure slightly higher than an expected diastolic pressure, and closes the air vent valve to decrease the pressure release rate to reduce the cuff pressure and thus determine the diastolic pressure by confirming ceasing of K-sounds.
Some electronic sphygmomanometers detect K-sounds in a decompression process in which the air is discharged at a slow rate and accordingly determine the systolic pressure by a corresponding cuff pressure, then increase the pressure release rate to a constant fast rate so as to decrease the pressure to the one slightly higher than an expected diastolic pressure, and thereafter return the pressure release rate to the original slow rate and accordingly confirm ceasing of K-sounds to determine the diastolic pressure (see Japanese Patent Publication No. 57-5540).
The pressure release rate of the conventional mercury sphygmomanometer is adjusted directly by manual rotation of a dial in order to control the degree of opening of the air vent valve. After the pressure release rate is increased, if the valve is excessively closed in order to lower the rate to the original slow rate, the decompression could be stopped or the rate could be too slow resulting in a prolonged measurement time. In this case, much skill could be required for measurement. On the other hand, the electronic sphygmomanometer switches the pressure release rate based on a preset cuff pressure with respect to a preset pressure release rate. Therefore, a skilled operator cannot select a pressure release rate based on the operator's experience or according to a subject person.